Data Link Protocols
•1
Relates to Lab 2.
This module covers data link layer issues, such as local area networks
(LANs) and point-to-point links, Ethernet, and the Point-to-Point Protocol
(PPP).
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Data Link Layer: Understanding Ethernet, MAC, LLC, and IEEE 802 Standards, Slides of Internet and Information Access
An in-depth exploration of the data link layer, focusing on ethernet, media access control (mac), logical link control (llc), and ieee 802 standards. Topics include the roles of mac and llc, bus and point-to-point networks, ethernet topologies, and various physical layer standards.
Typology: Slides
2012/2013
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Data Link Protocols
- 1
Relates to Lab 2.
This module covers data link layer issues, such as local area networks (LANs) and point-to-point links, Ethernet, and the Point-to-Point Protocol (PPP).
TCP/IP Suite and OSI Reference Model
Application Layer
Transport Layer Network Layer (Data) Link Layer
- The TCP/IP protocol stack does not
define the lower layers of a complete
protocol stack
- In this lecture, we will address how
the TCP/IP protocol stacks
interfaces with the data link layer
Logical Link Control (LLC) Media Access Control (MAC)
Sublayer in Local Area Networks
Two types of networks at the data link
layer
- Broadcast Networks: All stations share a single communication channel
- Point-to-Point Networks: Pairs of hosts (or routers) are directly connected
- Typically, local area networks (LANs) are broadcast and wide area networks (WANs) are point-to-point
Broadcast Network Point-to-Point Network
Local Area Networks
• Local area networks (LANs) connect
computers within a building or a enterprise
network
• Almost all LANs are broadcast networks
• Typical topologies of LANs are bus or ring or
star
• We will work with Ethernet LANs. Ethernet has
a bus or star topology.
Bus LAN Ring LAN
IEEE 802 Standards
• IEEE 802 is a family of standards for LANs,
which defines an LLC and several MAC
sublayers
802.3 802.4 802.5^ 802.
IEEE 802 standard
Medium Access Control Physical Layer
Logical Link Control
IEEE Reference Model
Physical Layer
Data Link Layer
Higher Layer
Ethernet
• Speed: 10Mbps -10 Gbps
• Standard: 802.3, Ethernet II (DIX)
• Most popular physical layers for Ethernet:
- 10Base5 Thick Ethernet: 10 Mbps coax cable
- 10Base2 Thin Ethernet: 10 Mbps coax cable
- 10Base-T 10 Mbps Twisted Pair
- 100Base-TX 100 Mbps over Category 5 twisted pair
- 100Base-FX 100 Mbps over Fiber Optics
- 1000Base-FX 1Gbps over Fiber Optics
- 10000Base-FX 1Gbps over Fiber Optics (for wide area links)
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Star Topology
• Starting with 10Base-T, stations are connected
to a hub in a star configuration
Hub
Ethernet Hubs vs. Ethernet Switches
- An Ethernet switch is a packet switch for Ethernet frames
- Buffering of frames prevents collisions.
- Each port is isolated and builds its own collision domain
- An Ethernet Hub does not perform buffering:
Collisions occur if two frames arrive at the same time.
Backplane^ HighSpeed
CSMA/CD CSMA/CD CSMA/CD CSMA/CD
CSMA/CD CSMA/CD CSMA/CD CSMA/CD
Output Buffers Input Buffers
CSMA/CD
CSMA/CD
CSMA/CD
CSMA/CD
CSMA/CD CSMA/CD CSMA/CD CSMA/CD
Hub Switch
Ethernet II, DIX Encapsulation (RFC
802.3 MAC
destination address 6
source address 6
type 2
data 46-
CRC 4
0800 2
IP datagram 38- 0806 2
ARP request/reply 28
PAD 10
0835 2
RARP request/reply 28
PAD 10
IEEE 802.2/802.3 Encapsulation (RFC
802.3 MAC destination address 6
source address 6
length 2
DSAP AA 1
SSAP AA 1
cntl 03 1
org code 0 3
type 2
data 38-
CRC 4
802.2 LLC 802.2 SNAP
- destination address, source address: MAC addresses are 48 bit
- length : frame length in number of bytes
- DSAP, SSAP : always set to 0xaa
- Ctrl: set to 3
- org code: set to 0
- type field identifies the content of the data field
- CRC: cylic redundancy check
0800 2
IP datagram 38- 0806 2
ARP request/reply 28
PAD 10 0835 2
RARP request/reply 28
PAD 10
Data Link Protocols for Point-to-Point
links
- SLIP (Serial Line IP)
- First protocol for sending IP datagrams over dial-up links (from 1988)
- Encapsulation, not much else
- PPP (Point-to-Point Protocol):
- Successor to SLIP (1992), with added functionality
- Used for dial-in and for high-speed routers
- HDLC (High-Level Data Link) :
- Widely used and influential standard (1979)
- Default protocol for serial links on Cisco routers
- Actually, PPP is based on a variant of HDLC
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PPP - IP encapsulation
- The frame format of PPP is similar to HDLC and the 802.2 LLC frame format:
- PPP assumes a duplex circuit
- Note: PPP does not use addresses
Usual maximum frame size is 1500
7E
flag
1
FF
addr
1
03
ctrl
1 2
protocol
<= 1500
data
2
CRC 7E
flag
1
0021 IP datagram
C021 link control data
8021 network control data
PPP Support protocols
• Link management: The link control protocol (LCP) is
responsible for establishing, configuring, and
negotiating a data-link connection. LCP also monitors
the link quality and is used to terminate the link.
• Authentication: Authentication is optional. PPP
supports two authentication protocols: Password
Authentication Protocol (PAP) and Challenge Handshake
Authentication Protocol (CHAP).
• Network protocol configuration: PPP has network
control protocols (NCPs) for numerous network layer
protocols. The IP control protocol (IPCP) negotiates IP
address assignments and other parameters when IP is
used as network layer.
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Switched networks
• Some data link technologies can be used to
build complete networks, with their own
addressing, routing, and forwarding
mechanisms. These networks are often called
switched networks.
• At the IP layer, a switched network may like a
point-to-point link or like a broadcast link
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