Layer 2 WAN Protocols
Before Layer 2 frames can be sent across the wire the IP Packet has to encapsulated with the correct Layer 2 framing format before crossing the WAN link. The process of switching out or replacing Layer 2 encapsulation (Framing and Header) with another Layer 2 frame is often referred to as Packet Switching. To ensure that the correct Layer 2 protocol is used, you need to configure the appropriate Layer 2 encapsulation type.
HDLC
High Level Data Link Control or HDLC is a bit oriented synchronous data link layer protocol developed by ISO. Derived from SDLC, HDLC specifies a data encapsulation method on synchronous serial links using frame characters and checksums.
ATM
Asynchronous Transfer Mode or ATM is an International Telecommunication Union-Telecommunications Standards Section (ITU-T) standard for cell relay wherein information for multiple service types (ie: voice, video, or data), is conveyed in small, fixed-size (53 byte) cells via connection-oriented Virtual Circuits or VCs. Unfortunately I have never had the opportunity to work with ATM.
Frame Relay
Frame Relay is an industry-standard, switched data link layer protocol that handles multiple virtual circuits. These circuits are refered to as Permanent Virtual Circuits or PVC’s. Frame Relay is much more efficient than traditional X.25, the protocol for which it is generally considered a replacement.
- Physical Interfaces
- Point To Point Subinterfaces
- Point To Multipoint Subinterfaces
- Layer 2 Encapsulations – Cisco, and IETF
- PVC – DLCI
- LMI messages every 10 seconds, 6th message full status
- LMI Types – Cisco, Q933a, and ITU
- LAPF Header – Bearer Services
- Inverse Arp – Maps Layer 2 DLCI’s to Layer 3 IP Addresses
- Congestion at Layer 2 – Adaptive shaping with BECN’s and FECN’s
PPP
The Point to Point Protocol or PPP, as described in RFC 1661, provides an encapsulation protocol for transporting network layer traffic over point-to-point links, such as synchronous serial or Integrated Services Digital Network or ISDN. Multilink PPP or MLP, as defined in RFC 1990, is a variant of PPP used to aggregate multiple WAN links into one logical channel for the transport of traffic. It enables the load-balancing of traffic from different links and allows some level of redundancy in case of a line failure on a single link.
- PPPoE Header size = 8 bytes
- PPPoE MTU size = 1492
Optical Carrier Transmission
Optical Carrier Transmission or OC is the term or technology used by Service Providers or Carriers on networks called Synchronous Optical Networks or SONET. Often refereed to as SONET Rings due to the optical nature of their architecture and redundancy. The bandwidths or rates are defined as bit stream of the digital signal or light.
OC Ring Protocols
- SONET – Synchronous Optical Network
- DWDM – Dense Wave Division Multiplexing
OC Features
- Long Distances
- Recognized International Standard
- Supports Voice, Video, and Data
- Fault Tolerant
OC Ring Units Of Measure
- OC1 bandwidth 51.84 Mbit/s or 33 T1’s
- OC3 bandwidth 155.52 Mbit/s or 100 T1’s
- OC12 bandwidth 622.08 Mbit/s or 403 T1’s
- OC48 bandwidth 2488.32 Mbit/s or 1615 T1’s
- OC192 bandwidth 9953.28 Mbit/s or 6462 T1’s
- OC768 bandwidth 39,813.12 Mbit/s or 25852 T1’s
I hope you found this post on WAN Protocols helpful and informative. Be sure to let me know what you think by leaving suggestions, and feedback in the comments section below. You can find out more about these and other articles be checking out recent posts and archives. To learn more about me be sure to check out the About page. And as always thanks again for visiting The Packet.
