Q) What exactly is “Carrier Ethernet” and how is it different than plain vanilla “Ethernet”?
A: The term “Carrier Ethernet” has evolved over the years. It used to refer
to any network carrying Ethernet that had 5-nines reliability. Then, it meant
Ethernet hardware that had a few Carrier nice-to-haves, such as in-service software upgrades. Recently, the term has referred to Ethernet services that meet a set of criteria as defined by the MEF, the Metro Ethernet Forum.
The Ethernet Alliance would define “Carrier Ethernet” a bit more
generically, as any Ethernet product or service that meets the demands of
Carriers, with the acknowledgement that Carriers needs are constantly
changing. While the MEF is focused primarily enabling the wholesaling of
Ethernet services, the Ethernet Alliance will be addressing all aspects of
Carrier Ethernet.
Q) OK, well enough, but then what are the needs of Carriers and how is Carrier Ethernet different?
A: Carrier Ethernet appends standard Enterprise Ethernet with additional
features and protocols that provide the capabilities they need to deliver
services to their customers.
For example, in traditional Ethernet, each end-user has their own MAC
address, which works great for LAN’s. However, when Carriers start
transporting millions of user’s data traffic, there is a need for MAC address
isolation. While in an ideal world, everyone has a unique MAC address,
unfortunately that is not always the case as sometimes NIC’s and the MAC
addresses embedded in them have been cloned. Ethernet’s traditional flat
addressing scheme can wreak havoc when two independent LAN’s have
been interconnected by a Carrier. IEEE standard 802.1ah, also known as
MAC-in-MAC, solves this problem with hierarchical MAC addressing,
allowing a Carrier to encapsulate the Ethernet it is transporting, preventing
MAC address collisions.
Q) Are there additional examples of where Carrier Ethernet differs from Enterprise offerings?
A: Carriers often carry video traffic destined for a subset of users.
Distribution of this type of content is usually by multicast, whereby the same packets are sent to all the multicast (IGMP) listeners. While this is not a problem for Layer 3 and above IP Routers that are aware of who the
listeners are, this can be disastrous for traditional Layer 2 Ethernet switches, which automatically flood all ports with any and all multicast traffic that enters any single port. A single video stream on a single port can consume all of the available bandwidth of the switch. A Carrier Ethernet switch uses IGMP snooping to look at the ports and determine which ones do and do not have an IGMP listener, and will flood the multicast traffic only to those ports that actually want to receive them.
Another example would be VLAN tagging. Traditional Ethernet uses a 12-
bitVLAN field, which yields 4095 VLAN tags, which is more than enough
for traditional Enterprise LAN’s. However, Carriers use VLAN tags to
differentiate between customers and services, and with the onslaught of
triple-play, HDTV, VoD, etc, 4095 is simply not enough tags. Carrier
Ethernet networks support double-tagging, also known as QinQ, where the
packets contain both an outer and inner VLAN identifier, thus vastly
increasing the number of VLAN tags supported.
Q) Where does Carrier Ethernet stand today?
A: Ethernet has grown over the years from being a LAN protocol into
practically all areas of communication. Today, Ethernet is the protocol of
choice for Carriers, in their GMPLS backbones, their Metropolitan DWDM
networks, and even their local access loops. However, there is still much
work to be done. As Carrier needs change, so must Ethernet continue to
evolve to meet these new demands.
Q) What is next for Carrier Ethernet?
A: With bandwidth consumption showing no signs of slowing, Carrier
Ethernet networks are struggling to scale fast enough, so scalability is a
continuing area of need. As these networks scale frighteningly fast,
efficiency becomes another key area of need. For example, if you move
from 10-10GE ports/links to 100, you may not necessarily have increased
your throughput 10X. Latency is increasingly becoming a new yet important
need, as the internet and computing experience continues to become more
real-time and high-performance computing clusters outgrow their buildings
and become more distributed.
Q) How can I become more involved in Carrier Ethernet and contribute to its success?
A: Consider joining the Ethernet Alliance, and specifically the Carrier
Ethernet Subcommittee. If your company is already a member of the
Ethernet Alliance, then simply go online and sign-up. If your company has
not yet joined, then you can still go online, fill out an application, and join
the Carrier Ethernet Subcommittee meetings as our guest while your
company considers the benefits of membership. And, be sure to notice the
RSS feed that will bring our work right to your desktop, live as it occurs.