diff --git a/pysnmp/debug.py b/pysnmp/debug.py
index 6889cd74e..1ec8c7188 100644
--- a/pysnmp/debug.py
+++ b/pysnmp/debug.py
@@ -5,7 +5,8 @@
 # License: https://www.pysnmp.com/pysnmp/license.html
 #
 import logging
-from pyasn1.compat.octets import octs2ints
+
+
 from pysnmp import error
 from pysnmp import __version__
 
@@ -129,6 +130,6 @@ def hexdump(octets):
     return " ".join(
         [
             "{}{:02X}".format(n % 16 == 0 and ("\n%.5d: " % n) or "", x)
-            for n, x in zip(range(len(octets)), octs2ints(octets))
+            for n, x in zip(range(len(octets)), octets)
         ]
     )
diff --git a/pysnmp/entity/config.py b/pysnmp/entity/config.py
index 37cb50b44..a67aca2e0 100644
--- a/pysnmp/entity/config.py
+++ b/pysnmp/entity/config.py
@@ -4,7 +4,6 @@
 # Copyright (c) 2005-2020, Ilya Etingof <etingof@gmail.com>
 # License: https://www.pysnmp.com/pysnmp/license.html
 #
-from pyasn1.compat.octets import null
 from pysnmp.carrier.asyncio.dgram import udp, udp6, unix
 from pysnmp.carrier.base import AbstractTransport
 from pysnmp.entity.engine import SnmpEngine
@@ -117,7 +116,7 @@ def addV1System(
         contextEngineId = snmpEngineID.syntax.clone(contextEngineId)
 
     if contextName is None:
-        contextName = null
+        contextName = b""
 
     securityName = securityName is not None and securityName or communityIndex
 
@@ -258,7 +257,7 @@ def addV3User(
     masterAuthKey = localAuthKey = authKey
 
     if authKeyType < usmKeyTypeMaster:  # pass phrase is given
-        masterAuthKey = authServices[authProtocol].hashPassphrase(authKey or null)
+        masterAuthKey = authServices[authProtocol].hashPassphrase(authKey or b"")
 
     if authKeyType < usmKeyTypeLocalized:  # pass phrase or master key is given
         localAuthKey = authServices[authProtocol].localizeKey(
@@ -275,7 +274,7 @@ def addV3User(
 
     if privKeyType < usmKeyTypeMaster:  # pass phrase is given
         masterPrivKey = privServices[privProtocol].hashPassphrase(
-            authProtocol, privKey or null
+            authProtocol, privKey or b""
         )
 
     if privKeyType < usmKeyTypeLocalized:  # pass phrase or master key is given
@@ -468,7 +467,7 @@ def addTargetAddr(
     params: str,
     timeout: "float | None" = None,
     retryCount: "int | None" = None,
-    tagList=null,
+    tagList=b"",
     sourceAddress=None,
 ):
     mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
@@ -776,7 +775,7 @@ def addVacmUser(
     readSubTree=(),
     writeSubTree=(),
     notifySubTree=(),
-    contextName=null,
+    contextName=b"",
 ):
     (groupName, securityLevel, readView, writeView, notifyView) = __cookVacmUserInfo(
         snmpEngine, securityModel, securityName, securityLevel
@@ -795,11 +794,11 @@ def addVacmUser(
         notifyView,
     )
     if readSubTree:
-        addVacmView(snmpEngine, readView, "included", readSubTree, null)
+        addVacmView(snmpEngine, readView, "included", readSubTree, b"")
     if writeSubTree:
-        addVacmView(snmpEngine, writeView, "included", writeSubTree, null)
+        addVacmView(snmpEngine, writeView, "included", writeSubTree, b"")
     if notifySubTree:
-        addVacmView(snmpEngine, notifyView, "included", notifySubTree, null)
+        addVacmView(snmpEngine, notifyView, "included", notifySubTree, b"")
 
 
 def delVacmUser(
@@ -810,7 +809,7 @@ def delVacmUser(
     readSubTree=(),
     writeSubTree=(),
     notifySubTree=(),
-    contextName=null,
+    contextName=b"",
 ):
     (groupName, securityLevel, readView, writeView, notifyView) = __cookVacmUserInfo(
         snmpEngine, securityModel, securityName, securityLevel
@@ -830,7 +829,7 @@ def delVacmUser(
 
 
 def addRoUser(
-    snmpEngine, securityModel, securityName, securityLevel, subTree, contextName=null
+    snmpEngine, securityModel, securityName, securityLevel, subTree, contextName=b""
 ):
     addVacmUser(
         snmpEngine,
@@ -843,7 +842,7 @@ def addRoUser(
 
 
 def delRoUser(
-    snmpEngine, securityModel, securityName, securityLevel, subTree, contextName=null
+    snmpEngine, securityModel, securityName, securityLevel, subTree, contextName=b""
 ):
     delVacmUser(
         snmpEngine,
@@ -856,7 +855,7 @@ def delRoUser(
 
 
 def addRwUser(
-    snmpEngine, securityModel, securityName, securityLevel, subTree, contextName=null
+    snmpEngine, securityModel, securityName, securityLevel, subTree, contextName=b""
 ):
     addVacmUser(
         snmpEngine,
@@ -870,7 +869,7 @@ def addRwUser(
 
 
 def delRwUser(
-    snmpEngine, securityModel, securityName, securityLevel, subTree, contextName=null
+    snmpEngine, securityModel, securityName, securityLevel, subTree, contextName=b""
 ):
     delVacmUser(
         snmpEngine,
@@ -884,7 +883,7 @@ def delRwUser(
 
 
 def addTrapUser(
-    snmpEngine, securityModel, securityName, securityLevel, subTree, contextName=null
+    snmpEngine, securityModel, securityName, securityLevel, subTree, contextName=b""
 ):
     addVacmUser(
         snmpEngine,
@@ -899,7 +898,7 @@ def addTrapUser(
 
 
 def delTrapUser(
-    snmpEngine, securityModel, securityName, securityLevel, subTree, contextName=null
+    snmpEngine, securityModel, securityName, securityLevel, subTree, contextName=b""
 ):
     delVacmUser(
         snmpEngine,
diff --git a/pysnmp/entity/engine.py b/pysnmp/entity/engine.py
index 3986b6d31..3ff95278c 100644
--- a/pysnmp/entity/engine.py
+++ b/pysnmp/entity/engine.py
@@ -9,7 +9,6 @@
 import sys
 import tempfile
 from typing import Any
-from pyasn1.compat.octets import str2octs
 from pysnmp.carrier.base import AbstractTransportAddress, AbstractTransportDispatcher
 from pysnmp.proto.rfc1902 import OctetString
 from pysnmp.proto.rfc3412 import MsgAndPduDispatcher
@@ -157,7 +156,7 @@ def __init__(
 
             try:
                 fd, fn = tempfile.mkstemp(dir=persistentPath)
-                os.write(fd, str2octs(snmpEngineBoots.syntax.prettyPrint()))
+                os.write(fd, snmpEngineBoots.syntax.prettyPrint().encode("iso-8859-1"))
                 os.close(fd)
                 shutil.move(fn, f)
             except Exception:
diff --git a/pysnmp/entity/rfc3413/context.py b/pysnmp/entity/rfc3413/context.py
index c65584da8..2c2547a6a 100644
--- a/pysnmp/entity/rfc3413/context.py
+++ b/pysnmp/entity/rfc3413/context.py
@@ -5,7 +5,6 @@
 # License: https://www.pysnmp.com/pysnmp/license.html
 #
 from pyasn1.type import univ
-from pyasn1.compat.octets import null
 from pysnmp import error
 from pysnmp import debug
 
@@ -26,7 +25,7 @@ def __init__(self, snmpEngine, contextEngineId=None):
             f'SnmpContext: contextEngineId "{self.contextEngineId!r}"'
         )
         self.contextNames = {
-            null: snmpEngine.msgAndPduDsp.mibInstrumController  # Default name
+            b"": snmpEngine.msgAndPduDsp.mibInstrumController  # Default name
         }
 
     def registerContextName(self, contextName, mibInstrum=None):
@@ -37,7 +36,7 @@ def registerContextName(self, contextName, mibInstrum=None):
             f"registerContextName: registered contextName {contextName!r}, mibInstrum {mibInstrum!r}"
         )
         if mibInstrum is None:
-            self.contextNames[contextName] = self.contextNames[null]
+            self.contextNames[contextName] = self.contextNames[b""]
         else:
             self.contextNames[contextName] = mibInstrum
 
@@ -49,7 +48,7 @@ def unregisterContextName(self, contextName):
             )
             del self.contextNames[contextName]
 
-    def getMibInstrum(self, contextName=null):
+    def getMibInstrum(self, contextName=b""):
         contextName = univ.OctetString(contextName).asOctets()
         if contextName not in self.contextNames:
             debug.logger & debug.flagIns and debug.logger(
diff --git a/pysnmp/entity/rfc3413/ntforg.py b/pysnmp/entity/rfc3413/ntforg.py
index d0f2795fa..73c7df8cc 100644
--- a/pysnmp/entity/rfc3413/ntforg.py
+++ b/pysnmp/entity/rfc3413/ntforg.py
@@ -5,7 +5,6 @@
 # License: https://www.pysnmp.com/pysnmp/license.html
 #
 import sys
-from pyasn1.compat.octets import null
 from pysnmp.entity.rfc3413 import config
 from pysnmp.proto.proxy import rfc2576
 from pysnmp.proto import rfc3411
@@ -564,7 +563,7 @@ def _sendNotification(
     additionalVarBinds=(),
     cbFun=None,
     cbCtx=None,
-    contextName=null,
+    contextName=b"",
     instanceIndex=None,
 ):
     if self.snmpContext is None:
diff --git a/pysnmp/entity/rfc3413/ntfrcv.py b/pysnmp/entity/rfc3413/ntfrcv.py
index 73450e9b4..43200b9c9 100644
--- a/pysnmp/entity/rfc3413/ntfrcv.py
+++ b/pysnmp/entity/rfc3413/ntfrcv.py
@@ -5,7 +5,6 @@
 # License: https://www.pysnmp.com/pysnmp/license.html
 #
 import sys
-from pyasn1.compat.octets import null
 from pysnmp.proto import rfc3411, error
 from pysnmp.proto.api import v1, v2c  # backend is always SMIv2 compliant
 from pysnmp.proto.proxy import rfc2576
@@ -22,7 +21,7 @@ class NotificationReceiver:
 
     def __init__(self, snmpEngine, cbFun, cbCtx=None):
         snmpEngine.msgAndPduDsp.registerContextEngineId(
-            null, self.pduTypes, self.processPdu  # '' is a wildcard
+            b"", self.pduTypes, self.processPdu  # '' is a wildcard
         )
 
         self.__snmpTrapCommunity = ""
@@ -38,7 +37,7 @@ def storeSnmpTrapCommunity(snmpEngine, execpoint, variables, cbCtx):
         )
 
     def close(self, snmpEngine):
-        snmpEngine.msgAndPduDsp.unregisterContextEngineId(null, self.pduTypes)
+        snmpEngine.msgAndPduDsp.unregisterContextEngineId(b"", self.pduTypes)
         self.__cbFun = self.__cbCtx = None
 
     def processPdu(
diff --git a/pysnmp/entity/rfc3413/oneliner/cmdgen.py b/pysnmp/entity/rfc3413/oneliner/cmdgen.py
index abdb59c14..560f8ffa7 100644
--- a/pysnmp/entity/rfc3413/oneliner/cmdgen.py
+++ b/pysnmp/entity/rfc3413/oneliner/cmdgen.py
@@ -13,7 +13,6 @@
 from pysnmp.hlapi.asyncio import sync
 from pysnmp.hlapi.varbinds import *
 from pysnmp.hlapi.lcd import *
-from pyasn1.compat.octets import null
 from pyasn1.type import univ
 
 __all__ = ["CommandGenerator", "MibVariable"]
@@ -37,7 +36,7 @@ def getCmd(self, authData, transportTarget, *varNames, **kwargs):
             self.snmpEngine,
             authData,
             transportTarget,
-            ContextData(kwargs.get("contextEngineId"), kwargs.get("contextName", null)),
+            ContextData(kwargs.get("contextEngineId"), kwargs.get("contextName", b"")),
             *[(x, self._null) for x in varNames],
             **kwargs
         )
@@ -51,7 +50,7 @@ def setCmd(self, authData, transportTarget, *varBinds, **kwargs):
             self.snmpEngine,
             authData,
             transportTarget,
-            ContextData(kwargs.get("contextEngineId"), kwargs.get("contextName", null)),
+            ContextData(kwargs.get("contextEngineId"), kwargs.get("contextName", b"")),
             *varBinds,
             **kwargs
         )
@@ -69,7 +68,7 @@ def nextCmd(self, authData, transportTarget, *varNames, **kwargs):
             self.snmpEngine,
             authData,
             transportTarget,
-            ContextData(kwargs.get("contextEngineId"), kwargs.get("contextName", null)),
+            ContextData(kwargs.get("contextEngineId"), kwargs.get("contextName", b"")),
             *[(x, self._null) for x in varNames],
             **kwargs
         ):
@@ -101,7 +100,7 @@ def bulkCmd(
             self.snmpEngine,
             authData,
             transportTarget,
-            ContextData(kwargs.get("contextEngineId"), kwargs.get("contextName", null)),
+            ContextData(kwargs.get("contextEngineId"), kwargs.get("contextName", b"")),
             nonRepeaters,
             maxRepetitions,
             *[(x, self._null) for x in varNames],
diff --git a/pysnmp/entity/rfc3413/oneliner/ntforg.py b/pysnmp/entity/rfc3413/oneliner/ntforg.py
index e35f34b12..47f6a3368 100644
--- a/pysnmp/entity/rfc3413/oneliner/ntforg.py
+++ b/pysnmp/entity/rfc3413/oneliner/ntforg.py
@@ -13,7 +13,6 @@
 from pysnmp.hlapi.asyncio import sync
 from pysnmp.hlapi.varbinds import *
 from pysnmp.hlapi.lcd import *
-from pyasn1.compat.octets import null
 from pysnmp.entity import config
 from pysnmp.entity.rfc3413 import context
 
@@ -82,7 +81,7 @@ def sendNotification(
             self.snmpEngine,
             authData,
             transportTarget,
-            ContextData(kwargs.get("contextEngineId"), kwargs.get("contextName", null)),
+            ContextData(kwargs.get("contextEngineId"), kwargs.get("contextName", b"")),
             notifyType,
             notificationType.addVarBinds(*varBinds),
             **kwargs
diff --git a/pysnmp/hlapi/auth.py b/pysnmp/hlapi/auth.py
index cb80a7908..8f8172856 100644
--- a/pysnmp/hlapi/auth.py
+++ b/pysnmp/hlapi/auth.py
@@ -6,7 +6,7 @@
 #
 from pysnmp.entity import config
 from pysnmp import error
-from pyasn1.compat.octets import null
+
 
 __all__ = [
     "CommunityData",
@@ -113,8 +113,8 @@ class instance.
     mpModel = 1  # Default is SMIv2
     securityModel = mpModel + 1
     securityLevel = "noAuthNoPriv"
-    contextName = null
-    tag = null
+    contextName = b""
+    tag = b""
 
     def __init__(
         self,
@@ -381,7 +381,7 @@ class instance.
     securityLevel = "noAuthNoPriv"
     securityModel = 3
     mpModel = 3
-    contextName = null
+    contextName = b""
 
     def __init__(
         self,
diff --git a/pysnmp/hlapi/context.py b/pysnmp/hlapi/context.py
index 352c78e6d..babb9fea7 100644
--- a/pysnmp/hlapi/context.py
+++ b/pysnmp/hlapi/context.py
@@ -4,8 +4,6 @@
 # Copyright (c) 2005-2020, Ilya Etingof <etingof@gmail.com>
 # License: https://www.pysnmp.com/pysnmp/license.html
 #
-from pyasn1.compat.octets import null
-
 __all__ = ["ContextData"]
 
 
@@ -46,7 +44,7 @@ class ContextData:
 
     """
 
-    def __init__(self, contextEngineId=None, contextName=null):
+    def __init__(self, contextEngineId=None, contextName=b""):
         self.contextEngineId = contextEngineId
         self.contextName = contextName
 
diff --git a/pysnmp/hlapi/lcd.py b/pysnmp/hlapi/lcd.py
index ff19ba144..53ce6066b 100644
--- a/pysnmp/hlapi/lcd.py
+++ b/pysnmp/hlapi/lcd.py
@@ -9,8 +9,6 @@
 from pysnmp.entity.engine import SnmpEngine
 from pysnmp.hlapi.auth import *
 
-from pyasn1.compat.octets import null
-
 from pysnmp.hlapi.transport import AbstractTransportTarget
 
 __all__ = ["CommandGeneratorLcdConfigurator", "NotificationOriginatorLcdConfigurator"]
@@ -39,7 +37,7 @@ class CommandGeneratorLcdConfigurator(AbstractLcdConfigurator):
     cacheKeys = ["auth", "parm", "tran", "addr"]
 
     def configure(
-        self, snmpEngine, authData, transportTarget, contextName=null, **options
+        self, snmpEngine, authData, transportTarget, contextName=b"", **options
     ):
         cache = self._getCache(snmpEngine)
         if isinstance(authData, CommunityData):
@@ -128,7 +126,7 @@ def configure(
 
         return addrName, paramsName
 
-    def unconfigure(self, snmpEngine, authData=None, contextName=null, **options):
+    def unconfigure(self, snmpEngine, authData=None, contextName=b"", **options):
         cache = self._getCache(snmpEngine)
         if authData:
             if isinstance(authData, CommunityData):
@@ -264,7 +262,7 @@ def configure(
 
         return notifyName
 
-    def unconfigure(self, snmpEngine, authData=None, contextName=null, **options):
+    def unconfigure(self, snmpEngine, authData=None, contextName=b"", **options):
         cache = self._getCache(snmpEngine)
         if authData:
             authDataKey = (
diff --git a/pysnmp/hlapi/transport.py b/pysnmp/hlapi/transport.py
index 49b9799e1..db79db276 100644
--- a/pysnmp/hlapi/transport.py
+++ b/pysnmp/hlapi/transport.py
@@ -5,7 +5,6 @@
 # License: https://www.pysnmp.com/pysnmp/license.html
 #
 from typing import Tuple
-from pyasn1.compat.octets import null
 from pysnmp.carrier.base import AbstractTransport, AbstractTransportAddress
 from pysnmp import error
 from pysnmp.entity.engine import SnmpEngine
@@ -27,7 +26,7 @@ def __init__(
         transportAddr: Tuple,
         timeout: float = 1,
         retries: int = 5,
-        tagList=null,
+        tagList=b"",
     ):
         self.transportAddr = self._resolveAddr(transportAddr)
         self.timeout = timeout
diff --git a/pysnmp/proto/mpmod/rfc2576.py b/pysnmp/proto/mpmod/rfc2576.py
index dbe65f86f..f916a1bbb 100644
--- a/pysnmp/proto/mpmod/rfc2576.py
+++ b/pysnmp/proto/mpmod/rfc2576.py
@@ -5,10 +5,11 @@
 # License: https://www.pysnmp.com/pysnmp/license.html
 #
 import sys
+
+
 from pyasn1.codec.ber import decoder, eoo
 from pyasn1.type import univ
-from pyasn1.compat.octets import null
-from pyasn1.error import PyAsn1Error
+
 from pysnmp.proto.mpmod.base import AbstractMessageProcessingModel
 from pysnmp.proto import rfc3411, errind, error
 from pysnmp.proto.api import v1, v2c
@@ -65,7 +66,7 @@ def prepareOutgoingMessage(
 
         # rfc3412: 7.1.5
         if not contextName:
-            contextName = null
+            contextName = b""
 
         debug.logger & debug.flagMP and debug.logger(
             f"prepareOutgoingMessage: using contextEngineId {contextEngineId!r} contextName {contextName!r}"
@@ -227,7 +228,7 @@ def prepareResponseMessage(
 
         # rfc3412: 7.1.5
         if not contextName:
-            contextName = null
+            contextName = b""
 
         # rfc3412: 7.1.6
         scopedPDU = (contextEngineId, contextName, pdu)
diff --git a/pysnmp/proto/rfc3412.py b/pysnmp/proto/rfc3412.py
index 94cac0054..e22e59a63 100644
--- a/pysnmp/proto/rfc3412.py
+++ b/pysnmp/proto/rfc3412.py
@@ -5,8 +5,10 @@
 # License: https://www.pysnmp.com/pysnmp/license.html
 #
 import sys
-from pyasn1.compat.octets import null
+
+
 from pyasn1.error import PyAsn1Error
+
 from pysnmp.smi import builder, instrum
 from pysnmp.proto import errind, error, cache
 from pysnmp.proto.api import verdec  # XXX
@@ -103,7 +105,7 @@ def getRegisteredApp(self, contextEngineId, pduType):
         k = (contextEngineId, pduType)
         if k in self.__appsRegistration:
             return self.__appsRegistration[k]
-        k = (null, pduType)
+        k = (b"", pduType)
         if k in self.__appsRegistration:
             return self.__appsRegistration[k]  # wildcard
 
@@ -362,7 +364,7 @@ def receiveMessage(self, snmpEngine, transportDomain, transportAddress, wholeMsg
 
         # 4.2.1.2
         try:
-            restOfWholeMsg = null  # XXX fix decoder non-recursive return
+            restOfWholeMsg = b""  # XXX fix decoder non-recursive return
             msgVersion = verdec.decodeMessageVersion(wholeMsg)
 
         except error.ProtocolError:
@@ -370,7 +372,7 @@ def receiveMessage(self, snmpEngine, transportDomain, transportAddress, wholeMsg
                 "__SNMPv2-MIB", "snmpInASNParseErrs"  # type: ignore
             )
             snmpInASNParseErrs.syntax += 1
-            return null  # n.b the whole buffer gets dropped
+            return b""  # n.b the whole buffer gets dropped
 
         debug.logger & debug.flagDsp and debug.logger(
             "receiveMessage: msgVersion %s, msg decoded" % msgVersion
diff --git a/pysnmp/proto/secmod/eso/priv/des3.py b/pysnmp/proto/secmod/eso/priv/des3.py
index 06448b556..e5e68af8b 100644
--- a/pysnmp/proto/secmod/eso/priv/des3.py
+++ b/pysnmp/proto/secmod/eso/priv/des3.py
@@ -6,14 +6,8 @@
 #
 import random
 
-try:
-    from hashlib import md5, sha1
-except ImportError:
-    import md5
-    import sha
+from hashlib import md5, sha1
 
-    md5 = md5.new
-    sha1 = sha.new
 
 try:
     from pysnmpcrypto import des3, PysnmpCryptoError
@@ -28,7 +22,7 @@
 from pysnmp.proto.secmod.rfc7860.auth import hmacsha2
 from pysnmp.proto import errind, error
 from pyasn1.type import univ
-from pyasn1.compat.octets import null
+
 
 random.seed()
 
diff --git a/pysnmp/proto/secmod/rfc3414/service.py b/pysnmp/proto/secmod/rfc3414/service.py
index 6f8e48398..a818c001b 100644
--- a/pysnmp/proto/secmod/rfc3414/service.py
+++ b/pysnmp/proto/secmod/rfc3414/service.py
@@ -21,7 +21,7 @@
 from pyasn1.type import univ, namedtype, constraint
 from pyasn1.codec.ber import encoder, decoder, eoo
 from pyasn1.error import PyAsn1Error
-from pyasn1.compat.octets import null
+
 
 # API to rfc1905 protocol objects
 pMod = api.protoModules[api.protoVersion2c]
@@ -494,12 +494,12 @@ def __generateRequestOrResponseMsg(
 
         else:
             # 4. (start SNMP engine ID discovery)
-            securityEngineID = securityName = null
+            securityEngineID = securityName = b""
             securityLevel = 1
 
             scopedPDU.setComponentByPosition(
                 0,
-                null,
+                b"",
                 verifyConstraints=False,
                 matchTags=False,
                 matchConstraints=False,
@@ -533,7 +533,7 @@ def __generateRequestOrResponseMsg(
                 matchConstraints=False,
             )
 
-            usmUserName = usmUserSecurityName = null
+            usmUserName = usmUserSecurityName = b""
             usmUserAuthProtocol = noauth.NoAuth.serviceID
             usmUserPrivProtocol = nopriv.NoPriv.serviceID
             usmUserAuthKeyLocalized = usmUserPrivKeyLocalized = None
@@ -955,7 +955,7 @@ def processIncomingMsg(
         contextEngineId = mibBuilder.importSymbols(
             "__SNMP-FRAMEWORK-MIB", "snmpEngineID"
         )[0].syntax
-        contextName = null
+        contextName = b""
 
         snmpEngineID = mibBuilder.importSymbols("__SNMP-FRAMEWORK-MIB", "snmpEngineID")[
             0
@@ -1106,7 +1106,7 @@ def processIncomingMsg(
                 raise error.StatusInformation(errorIndication=errind.invalidMsg)
         else:
             # empty username used for engineID discovery
-            usmUserName = usmUserSecurityName = null
+            usmUserName = usmUserSecurityName = b""
             usmUserAuthProtocol = noauth.NoAuth.serviceID
             usmUserPrivProtocol = nopriv.NoPriv.serviceID
             usmUserAuthKeyLocalized = usmUserPrivKeyLocalized = None
diff --git a/pysnmp/smi/mibs/SNMPv2-TC.py b/pysnmp/smi/mibs/SNMPv2-TC.py
index 8c4f98b7b..60287d59c 100644
--- a/pysnmp/smi/mibs/SNMPv2-TC.py
+++ b/pysnmp/smi/mibs/SNMPv2-TC.py
@@ -10,7 +10,6 @@
 from pysnmp.smi.error import *
 from pysnmp import debug
 from pyasn1.type import univ
-from pyasn1.compat import octets
 from pyasn1.type.base import Asn1Item
 
 OctetString, Integer, ObjectIdentifier = mibBuilder.importSymbols(
@@ -109,7 +108,7 @@ def prettyOut(self, value):  # override asn1 type method
             while runningValue and displayHint:
                 # 1
                 if displayHint[0] == "*":
-                    repeatIndicator = repeatCount = octets.oct2int(runningValue[0])
+                    repeatIndicator = repeatCount = runningValue[0]
                     displayHint = displayHint[1:]
                     runningValue = runningValue[1:]
                 else:
@@ -173,7 +172,7 @@ def prettyOut(self, value):  # override asn1 type method
                         while numberString:
                             number <<= 8
                             try:
-                                number |= octets.oct2int(numberString[0])
+                                number |= numberString[0]
                                 numberString = numberString[1:]
                             except Exception:
                                 raise SmiError(
@@ -280,20 +279,20 @@ def prettyIn(self, value):  # override asn1 type method
         ):
             numBase = {"x": 16, "d": 10, "o": 8}
             numDigits = {
-                "x": octets.str2octs(string.hexdigits),
-                "o": octets.str2octs(string.octdigits),
-                "d": octets.str2octs(string.digits),
+                "x": string.hexdigits.encode("iso-8859-1"),
+                "o": string.octdigits.encode("iso-8859-1"),
+                "d": string.digits.encode("iso-8859-1"),
             }
 
             # how do we know if object is initialized with display-hint
             # formatted text? based on "text" input maybe?
             # That boils down to `str` object on Py3 or `unicode` on Py2.
-            if octets.isStringType(value) and not octets.isOctetsType(value):
+            if isinstance(value, str) and not isinstance(value, bytes):
                 value = base.prettyIn(self, value)
             else:
                 return base.prettyIn(self, value)
 
-            outputValue = octets.str2octs("")
+            outputValue = b""
             runningValue = value
             displayHint = self.displayHint
 
@@ -345,7 +344,7 @@ def prettyIn(self, value):  # override asn1 type method
                 elif displayFormat in numBase:
                     if displaySep:
                         guessedOctetLength = runningValue.find(
-                            octets.str2octs(displaySep)
+                            displaySep.encode("iso-8859-1")
                         )
                         if guessedOctetLength == -1:
                             guessedOctetLength = len(runningValue)
@@ -359,7 +358,7 @@ def prettyIn(self, value):  # override asn1 type method
 
                     try:
                         num = int(
-                            octets.octs2str(runningValue[:guessedOctetLength]),
+                            runningValue[:guessedOctetLength].decode("iso-8859-1"),
                             numBase[displayFormat],
                         )
                     except Exception:
@@ -381,7 +380,7 @@ def prettyIn(self, value):  # override asn1 type method
 
                     num_as_bytes.reverse()
 
-                    outputValue += octets.ints2octs(num_as_bytes)
+                    outputValue += bytes(num_as_bytes)
 
                     if displaySep:
                         guessedOctetLength += 1
diff --git a/pysnmp/smi/mibs/SNMPv2-TM.py b/pysnmp/smi/mibs/SNMPv2-TM.py
index e35856ee1..8c65d4917 100644
--- a/pysnmp/smi/mibs/SNMPv2-TM.py
+++ b/pysnmp/smi/mibs/SNMPv2-TM.py
@@ -18,7 +18,6 @@
     inet_ntop = lambda x, y: inet_ntoa(y)
     inet_pton = lambda x, y: inet_aton(y)
 
-from pyasn1.compat.octets import int2oct, oct2int
 
 (OctetString,) = mibBuilder.importSymbols("ASN1", "OctetString")
 (
@@ -93,8 +92,8 @@ def prettyIn(self, value):
             # Wild hack -- need to implement TextualConvention.prettyIn
             value = (
                 inet_pton(AF_INET, value[0])
-                + int2oct((value[1] >> 8) & 0xFF)
-                + int2oct(value[1] & 0xFF)
+                + bytes((((value[1] >> 8) & 0xFF),))
+                + bytes(((value[1] & 0xFF),))
             )
         return OctetString.prettyIn(self, value)
 
@@ -104,7 +103,7 @@ def __asSocketAddress(self):
             v = self.asOctets()
             self.__tuple_value = (
                 inet_ntop(AF_INET, v[:4]),
-                oct2int(v[4]) << 8 | oct2int(v[5]),
+                v[4] << 8 | v[5],
             )
         return self.__tuple_value
 
diff --git a/pysnmp/smi/mibs/TRANSPORT-ADDRESS-MIB.py b/pysnmp/smi/mibs/TRANSPORT-ADDRESS-MIB.py
index 1155777e4..ae5782029 100644
--- a/pysnmp/smi/mibs/TRANSPORT-ADDRESS-MIB.py
+++ b/pysnmp/smi/mibs/TRANSPORT-ADDRESS-MIB.py
@@ -11,7 +11,6 @@
 # Using Python version 3.4.2 (v3.4.2:ab2c023a9432, Oct  5 2014, 20:42:22)
 #
 
-from pyasn1.compat.octets import int2oct, oct2int
 from pysnmp import error
 from pysnmp.carrier import sockfix
 import socket
@@ -358,8 +357,8 @@ def prettyIn(self, value):
             # Wild hack -- need to implement TextualConvention.prettyIn
             value = (
                 inet_pton(socket.AF_INET, value[0])
-                + int2oct((value[1] >> 8) & 0xFF)
-                + int2oct(value[1] & 0xFF)
+                + bytes((((value[1] >> 8) & 0xFF),))
+                + bytes(((value[1] & 0xFF),))
             )
         return OctetString.prettyIn(self, value)
 
@@ -369,7 +368,7 @@ def __asSocketAddress(self):
             v = self.asOctets()
             self.__tuple_value = (
                 inet_ntop(socket.AF_INET, v[:4]),
-                oct2int(v[4]) << 8 | oct2int(v[5]),
+                v[4] << 8 | v[5],
             )
         return self.__tuple_value
 
@@ -393,8 +392,8 @@ def prettyIn(self, value):
         if isinstance(value, tuple):
             value = (
                 inet_pton(socket.AF_INET6, value[0])
-                + int2oct((value[1] >> 8) & 0xFF)
-                + int2oct(value[1] & 0xFF)
+                + bytes((((value[1] >> 8) & 0xFF),))
+                + bytes(((value[1] & 0xFF),))
             )
         return OctetString.prettyIn(self, value)
 
@@ -406,7 +405,7 @@ def __asSocketAddress(self):
             v = self.asOctets()
             self.__tuple_value = (
                 inet_ntop(socket.AF_INET6, v[:16]),
-                oct2int(v[16]) << 8 | oct2int(v[17]),
+                v[16] << 8 | v[17],
                 0,  # flowinfo
                 0,
             )  # scopeid